The loading of railway tank cars with liquified gases under pressure, or flowable gases under pressure, or flowable materials for which it is necessary to exclude the escape of vapors, requires that the level of the flowable materials be measured within a sealed tank or vessel. It has been known in the art to utilize various types of mechanical float gauging devices and various types of electrical resistance gauging devices to monitor the level of flowable material being loading into a tank car. These devices generally have components that extend inside the vessel and require contact with the lading.
Microwave technology has been used to continually monitor liquid levels in a stationary vessel. An example of such a device is the CannonBear 1001 Microwave Level Transmitter manufactured by TN Technologies of Round Rock, Tex. This device includes a transceiver unit that is mounted on the top of the vessel and sends a low-level microwave beam toward the surface of liquid in the vessel. Microprocessor-based electronics calculate the time for the reflected signal to return to the transceiver unit to gauge the distance from the transceiver unit to the surface of the liquid in the vessel. The transceiver unit is permanently mounted to the outside of the vessel and a non-conductive and inert process seal or lens separates the transceiver unit from the vessel interior. The transceiver unit is connected to a transmitter electronics which may be remote from the transceiver. Each vessel has a process seal or lens and a transceiver unit permanently mounted thereto.
The advantage of utilizing microwave level transmitter technology to measure the level of flowable materials in a vessel is that no part of the system is in contact with the vessel contents. Also, process material coating, abrasion, temperature change, composition change, density change, and moisture change do not affect the measurement.
There is a need for an improved method and apparatus that utilizes known microwave gauging technology to monitor the level of flowable material contained in a transportable vessel during the loading and unloading thereof at a loading/unloading facility.
As used herein the term "transportable vessel" is intended to include railway tank cars, highway tank trailers, cargo tanks, and the like.